Rotating image using objective C

Question

I am trying to rotate an image. This I am succeeding in doing. The problem is that when I am clicking down and dragging slightly, the image rotates completely to reach the point where I have clicked and then rotates slowly as I drag the image clockwise. I am concerned to why it is rotating completely to the place that I am dragging. I want the dragging to start from the position it is found and NOT to rotate to the place my finger is down on and then starts from there.

This is my code:

-

    (void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {   
    }

    -(void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
        NSSet *allTouches = [event allTouches];

        int len = [allTouches count]-1;

        UITouch *touch =[[allTouches allObjects] objectAtIndex:len];
        CGPoint location = [touch locationInView:[self superview]];
        float theAngle = atan2( location.y-self.center.y, location.x-self.center.x );

        totalRadians = theAngle;

        [self rotateImage:theAngle];

    }

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
}

-(void) rotateImage:(float)angleRadians{

    self.transform = CGAffineTransformMakeRotation(angleRadians);
    CATransform3D rotatedTransform = self.layer.transform;
    self.layer.transform = rotatedTransform;    
}

Am I doing anything wrong?

Thanks!

Answer 1

Instead of creating the transformation from the angle that your getting from the touch, try incrementing totalRadians by its difference from the new angle, and then create the transform from that.

-(void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
        NSSet *allTouches = [event allTouches];

        int len = [allTouches count]-1;

        UITouch *touch =[[allTouches allObjects] objectAtIndex:len];
        CGPoint location = [touch locationInView:[self superview]];
        float theAngle = atan2( location.y-self.center.y, location.x-self.center.x );

        totalRadians += fabs(theAngle - totalRadians);
        totalRadians = fmod(totalRadians, 2*M_PI);

        [self rotateImage:totalRadians];

    }

Answer 2

My first advice would be to switch to using the UIRotateGestureRecognizer if your app is for 4.0 and higher. It does the right thing and provides you with a rotation property.